Wikipedia ( /ˌwɪkɨˈpiːdiə / or /ˌwɪkiˈpiːdiə /WIK-i-PEE-dee-ə) is a collaboratively edited, multilingual, free Internet encyclopedia supported by the non-profit Wikimedia Foundation. Wikipedia's 26 million articles in 286 languages, including over 4.2 million in the English Wikipedia, are written collaboratively by volunteers around the world. Almost all of its articles can be edited by anyone with access to the site. It has become the largest and most popular general reference work on the Internet, ranking sixth globally among all websites on Alexa and having an estimated 365 million readers worldwide.

Wikipedia was launched on January 15, 2001, by Jimmy Wales and Larry Sanger. Sanger coined the name Wikipedia, which is a portmanteau of wiki (a type of collaborative website, from the Hawaiian word wiki, meaning "quick") and encyclopedia. Wikipedia's departure from the expert-driven style of encyclopedia building and the presence of a large body of unacademic content have received extensive attention in print media. In 2006, Time magazine recognized Wikipedia's participation in the rapid growth of online collaboration and interaction by millions of people around the world, in addition to YouTube, MySpace, and Facebook. Wikipedia has also been praised as a news source due to articles related to breaking news often being rapidly updated.

The open nature of Wikipedia has led to various concerns, such as the quality of writing, the amount of vandalism and the accuracy of information. Some articles contain unverified or inconsistent information, though a 2005 investigation in Nature showed that the science articles they compared came close to the level of accuracy of Encyclopædia Britannica and had a similar rate of "serious errors". Britannica replied that the study's methodology and conclusions were flawed, but Nature reacted to this refutation with both a formal response and a point-by-point rebuttal of Britannica's main objections.

Nature

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As the popular joke goes, ‘The problem with Wikipedia is that it only works in practice. In theory, it can never work.’

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—Miikka Ryökäs,

Editing

In April 2009, the Wikimedia Foundation conducted a Wikipedia usability study, questioning users about the editing mechanism.

In a departure from the style of traditional encyclopedias, Wikipedia is open to outside editing. This means that, with the exception of particularly sensitive and/or vandalism-prone pages that are "protected" to some degree, the reader of an article can edit the text without needing approval, doing so with a registered account or even anonymously. Different language editions modify this policy to some extent; for example, only registered users may create a new article in the English edition. No article is considered to be owned by its creator or any other editor, nor is it vetted by any recognized authority. Instead, editors are supposed to agree on the content and structure of articles by consensus.

By default, an edit to an article becomes available immediately, prior to any review. As such, an article may contain inaccuracies, ideological biases, or even patent nonsense, until or unless another editor corrects the problem. Different language editions, each under separate administrative control, are free to modify this policy. For example, the German Wikipedia maintains "stable versions" of articles, which have passed certain reviews. Following the protracted trials and community discussion, the "pending changes" system was introduced to English Wikipedia in December 2012. Under this system, new users' edits to certain controversial or vandalism-prone articles would be "subject to review from an established Wikipedia editor before publication".

Editors keep track of changes to articles by checking the difference between two revisions of a page, displayed here in yellow and blue.

Contributors, whether registered or not, can take advantage of features available in the software that powers Wikipedia. The "History" page belonging to each article records every single past revision of the article, though a revision with libelous content, criminal threats or copyright infringements may be removed retroactively. Editors can use this page to undo undesirable changes or restore lost content. The "Talk" page associated with each article helps coordinate work among multiple editors. Importantly, editors may use the "Talk" page to reach consensus, sometimes through the use of polling.

In addition, editors may view the most " recent changes" to the website, which are displayed in reverse chronology. Regular contributors often maintain a "watchlist" of articles of interest to them, in order to easily track recent changes to those articles. In language editions with many articles, editors tend to prefer the "watchlist" because the number of edits has become too large to follow in "recent changes." New page patrol is a process by which newly created articles are checked for obvious problems. A frequently vandalized article can be semi-protected, allowing only well established users to edit it. A particularly contentious article may be locked so that only administrators are able to make changes.

The editing interface of Wikipedia.

Computer programs called bots have been used widely to correct common misspellings and stylistic issues, or to start articles such as geography entries in a standard format from statistical data. There are also some bots designed to warn users making "undesirable" edits, block on the creation of links to particular websites, and block on edits from particular accounts or IP address ranges. Bots on Wikipedia must be approved by administration prior to activation.

Organization of article pages

Articles in Wikipedia are loosely organized according to their development status and subject matter. A new article often starts as a " stub", a very short page consisting of definitions and some links. On the other extreme, the most developed articles may be nominated for " Featured article" status. One "featured article" per day, as selected by editors, appears on the main page of Wikipedia. Researcher Giacomo Poderi found that articles tend to reach featured status via the intensive work of a few editors. A 2010 study found unevenness in quality among featured articles and concluded that the community process is ineffective in assessing the quality of articles. In 2007, in preparation for producing a print version, the English-language Wikipedia introduced an assessment scale against which the quality of articles is judged.

A group of Wikipedia editors may form a WikiProject to focus their work on a specific topic area, using its associated discussion page to coordinate changes across multiple articles.

Vandalism

Any edit that changes content in a way that deliberately compromises the integrity of Wikipedia is considered vandalism. The most common and obvious types of vandalism include insertion of obscenities and crude humor. Vandalism can also include advertising language, and other types of spam. Sometimes editors commit vandalism by removing information or entirely blanking a given page. Less common types of vandalism, such as the deliberate addition of plausible but false information to an article, can be more difficult to detect. Vandals can introduce irrelevant formatting, modify page semantics such as the page's title or categorization, manipulate the underlying code of an article, or utilize images disruptively.

The opportunity for vandalism provides a number of unique challenges to Wikipedia. One criticism is that, at any moment, a reader of an article cannot be certain that it has not been compromised by the insertion of false information or the removal of essential information. Former Encyclopædia Britannica editor-in-chief Robert McHenry once described the predicament using a simile:

The user who visits Wikipedia to learn about some subject, to confirm some matter of fact, is rather in the position of a visitor to a public restroom. It may be obviously dirty, so that he knows to exercise great care, or it may seem fairly clean, so that he may be lulled into a false sense of security. What he certainly does not know is who has used the facilities before him.

John Seigenthaler has described Wikipedia as "a flawed and irresponsible research tool".

Obvious vandalism is generally easy to remove from wiki articles; in practice, the median time to detect and fix vandalism is a few minutes. However, in one high-profile incident in 2005, false information was introduced into the biography of American political figure John Seigenthaler and remained undetected for four months. John Seigenthaler, the founding editorial director of USA Today and founder of the Freedom Forum First Amendment Centre at Vanderbilt University, called Wales and asked whether he had any way of knowing who contributed the misinformation. Wales replied that he did not, although the perpetrator was eventually traced. This incident led to policy changes on the site, specifically targeted at tightening up the verifiability of all biographical articles of living people.

Rules and laws governing content and editor behaviour

Content in Wikipedia is subject to the laws (in particular, the copyright laws) of the United States and of the U.S. state of Florida, where the majority of Wikipedia's servers are located. Beyond legal matters, the editorial principles of Wikipedia are embodied in the " five pillars", and numerous policies and guidelines that are intended to shape the content appropriately. Even these rules are stored in wiki form, and Wikipedia editors as a community write and revise the website's policies and guidelines. Editors can enforce rules by deleting or modifying non-compliant material. Originally, rules on the non-English editions of Wikipedia were based on a translation of the rules on the English Wikipedia. They have since diverged to some extent.

English Wikipedia

Content policies

According to the rules on the English Wikipedia, each entry in Wikipedia, to be worthy of inclusion, must be about a topic that is encyclopedic and is not a dictionary entry or dictionary-like. A topic should also meet Wikipedia's standards of " notability", which usually means that it must have received significant coverage in reliable secondary sources such as mainstream media or major academic journals that are independent of the subject of the topic. Further, Wikipedia intends to convey only knowledge that is already established and recognized. It must not present new information or original research. A claim that is likely to be challenged requires a reference to a reliable source. Among Wikipedia editors, this is often phrased as "verifiability, not truth" to express the idea that the readers, not the encyclopedia, are ultimately responsible for checking the truthfulness of the articles and making their own interpretations. This can lead to the removal of information that is valid, thus hindering inclusion of knowledge and growth of the encyclopedia. Finally, Wikipedia must not take sides. All opinions and viewpoints, if attributable to external sources, must enjoy an appropriate share of coverage within an article. This is known as neutral point of view ( NPOV).

Dispute resolution

Wikipedia has many methods of settling disputes. A "BOLD, revert, discuss" cycle sometimes occurs, in which an editor changes something, another editor reverts the change, and then the two editors discuss the issue on a talk page. When editors disregard this process – when a change is repeatedly done by one editor and then undone by another – an " edit war" may be asserted to have begun. The provenance of this term "edit war" is unknown.

In order to gain a broader community consensus, editors can raise issues at the Village Pump, or initiate a Request for Comment. An editor can report impolite, uncivil, or otherwise problematic communications with another editor via the " Wikiquette Assistance" noticeboard. Such postings themselves have no binding or disciplinary power. Specialized forums exist for centralizing discussion on specific decisions, such as whether or not an article should be deleted. Mediation is sometimes used, although it has been deemed by some Wikipedians to be unhelpful for resolving particularly contentious disputes.

Arbitration

The Arbitration Committee is the ultimate dispute resolution method. Although disputes usually arise from a disagreement between two opposing views on how articles should read, the Arbitration Committee explicitly refuses to directly rule on which view should be adopted. Statistical analyses suggest that the committee ignores the content of disputes and focuses on the way disputes are conducted instead, functioning not so much to resolve disputes and make peace between conflicting editors, but to weed out problematic editors while allowing potentially productive editors back in to participate. Therefore, the committee does not dictate the content of articles, although it sometimes condemns content changes when it deems the new content violates Wikipedia policies (for example, if the new content is biased). Its remedies include cautions and probations (used in 63.2% of cases) and banning editors from articles (43.3%), subject matters (23.4%) or Wikipedia (15.7%). Complete bans from Wikipedia are largely limited to instances of impersonation and anti-social behaviour. When conduct is not impersonation or anti-social, but rather anti-consensus or violating editing policies, warnings tend to be issued.

Privacy

One privacy concern in the case of Wikipedia is the right of a private citizen to remain private: to remain a "private citizen" rather than a " public figure" in the eyes of the law. It is a battle between the right to be anonymous in cyberspace and the right to be anonymous in real life (" meatspace"). A particular problem occurs in the case of an individual who is relatively unimportant and for whom there exists a Wikipedia page against her or his wishes.

In January 2006, a German court ordered the German Wikipedia shut down within Germany because it stated the full name of Boris Floricic, aka "Tron", a deceased hacker. On February 9, 2006, the injunction against Wikimedia Deutschland was overturned, with the court rejecting the notion that Tron's right to privacy or that of his parents were being violated.

Community

Wikimania, an annual conference for users of Wikipedia and other projects operated by the Wikimedia Foundation.

Wikipedia's community has been described as cult-like, although not always with entirely negative connotations, and criticized for failing to accommodate inexperienced users. The project's preference for cohesiveness, even if it requires compromise that includes disregard of credentials, has been referred to as " anti-elitism".

Power structure

The Wikipedia community has established "a bureaucracy of sorts", including "a clear power structure that gives volunteer administrators the authority to exercise editorial control." Editors in good standing in the community can run for one of many levels of volunteer stewardship: this begins with "administrator," a group of privileged users who have the ability to delete pages, lock articles from being changed in case of vandalism or editorial disputes, and block users from editing. Despite the name, administrators do not enjoy any special privilege in decision-making; instead, their powers are mostly limited to making edits that have project-wide effects and thus are disallowed to ordinary editors, and to block users making disruptive edits (such as vandalism). As the process of vetting potential Wikipedia administrators has become more rigorous, fewer editors are promoted to admin status than in years past.

Contributors

Demographics of Wikipedia editors.

Wikipedia does not require that its users provide identification. However, as Wikipedia grew, "Who writes Wikipedia?" became one of the questions frequently asked on the project, often with a reference to other Web 2.0 projects such as Digg. Wales once argued that only "a community ... a dedicated group of a few hundred volunteers" makes the bulk of contributions to Wikipedia and that the project is therefore "much like any traditional organization." Wales performed a study finding that over 50% of all the edits were done by just 0.7% of the users (at the time: 524 people). This method of evaluating contributions was later disputed by Aaron Swartz, who noted that several articles he sampled had large portions of their content (measured by number of characters) contributed by users with low edit counts. A 2007 study by researchers from Dartmouth College found that "anonymous and infrequent contributors to Wikipedia ... are as reliable a source of knowledge as those contributors who register with the site."

In 2003, economics PhD student Andrea Ciffolilli argued that the low transaction costs of participating in wiki software create a catalyst for collaborative development, and that such features as easy access to past versions of a page favour "creative construction" over "creative destruction". In his 2008 book, The Future of the Internet and How to Stop It, Zittrain cites Wikipedia's success as a case study in how open collaboration has fostered innovation on the web. A 2008 study found that Wikipedians were less agreeable, open, and conscientious than others. A 2009 study suggested there was "evidence of growing resistance from the Wikipedia community to new content."

At OOPSLA 2009, Wikimedia CTO and Senior Software Architect Brion Vibber gave a presentation entitled "Community Performance Optimization: Making Your People Run as Smoothly as Your Site" in which he discussed the challenges of handling the contributions from a large community and compared the process to that of software development.

Interactions

Wikipedians and British Museum curators collaborate on the article Hoxne Hoard in June 2010.

Members of the community interact with each other predominantly via 'talk' pages, which are wiki-edited pages that are associated with articles, as well as via talk pages that are specific to particular contributors, and talk pages that help run the site. These pages help the contributors reach consensus about what the contents of the articles should be, how the site's rules may change, and to take actions with respect to any problems within the community.

The Wikipedia Signpost is the community newspaper on the English Wikipedia, and was founded by Michael Snow, an administrator and the former chair of the Wikimedia Foundation board of trustees. It covers news and events from the site, as well as major events from sister projects, such as Wikimedia Commons.

Positive reinforcement

Wikipedians sometimes award one another barnstars for good work. These personalized tokens of appreciation reveal a wide range of valued work extending far beyond simple editing to include social support, administrative actions, and types of articulation work. The barnstar phenomenon has been analyzed by researchers seeking to determine what implications it might have for other communities engaged in large-scale collaborations.

New users

Up to sixty percent of Wikipedia's registered users never make another edit after their first 24 hours. Possible explanations are that such users register for only a single purpose, or are scared away by their experiences. Goldman writes that editors who fail to comply with Wikipedia cultural rituals, such as signing talk pages, implicitly signal that they are Wikipedia outsiders, increasing the odds that Wikipedia insiders will target their contributions as a threat. Becoming a Wikipedia insider involves non-trivial costs: the contributor is expected to build a user page, learn Wikipedia-specific technological codes, submit to an arcane dispute resolution process, and learn a "baffling culture rich with in-jokes and insider references." Non-logged-in users are in some sense second-class citizens on Wikipedia, as "participants are accredited by members of the wiki community, who have a vested interest in preserving the quality of the work product, on the basis of their ongoing participation," but the contribution histories of IP addresses cannot necessarily with any certainty be credited to, or blamed upon, a particular user.

A 2009 study by Business Insider editor and journalist Henry Blodget showed that in a random sample of articles most content in Wikipedia (measured by the amount of contributed text that survives to the latest sampled edit) is created by "outsiders" (users with low edit counts), while most editing and formatting is done by "insiders" (a select group of established users).

Demographics

Estimation of contributions shares from different regions in the world to different Wikipedia editions.

One study found that the contributor base to Wikipedia "was barely 13% women; the average age of a contributor was in the mid-20s." Sue Gardner, Executive Director of the Wikimedia Foundation, hopes to see female editing contributions increase to twenty-five percent by 2015. Linda Basch, President of the National Council for Research on Women, noted the contrast in these Wikipedia editor statistics with the percentage of women currently completing bachelor's degrees, master's degrees and PhD programs in the United States (all at rates of fifty percent or greater).

In a research article published in PLoS ONE in 2012, Yasseri et al., based on the circadian patterns of editorial activities of the community, have estimated the share of contributions to different editions of Wikipedia from different regions of the world. For instance, it has been reported that edits from North America are limited to almost 50% in the English Wikipedia and this value decreases to twenty-five percent in Simple English Wikipedia. The article also covers some other editions in different languages. The Wikimedia Foundation hopes to increase the number of editors in the Global South to thirty-seven percent by 2015.

Language editions

Percentage of all Wikipedia articles in English (red) and top ten largest language editions (blue). As of July 2007 less than 23% of Wikipedia articles are in English.

There are currently 285 language editions (or language versions) of Wikipedia; of these, five have over one million articles each ( English, German, French, Dutch and Italian), five more have over 700,000 articles ( Polish, Spanish, Russian, Japanese and Portuguese), 40 more have over 100,000 articles and 109 have over 10,000 articles. The largest, the English Wikipedia, has over 4.2 million articles. According to Alexa, the English subdomain (en.wikipedia.org; English Wikipedia) receives approximately 54% of Wikipedia's cumulative traffic, with the remaining split among the other languages (Japanese: 10%, German: 8%, Spanish: 5%, Russian: 4%, French: 4%, Italian: 3%). As of April 2013, the five largest language editions are (in order of article count) the English, German, Dutch, French, and Italian Wikipedias. The coexistence of multilingual content on Wikipedia is made possible by Unicode, whose support was first introduced into Wikipedia in January 2002 by Brion Vibber after he had similarly implemented the alphabet of Esperanto.

Since Wikipedia is web-based and therefore worldwide, contributors of a same language edition may use different dialects or may come from different countries (as is the case for the English edition). These differences may lead to some conflicts over spelling differences, (e.g. colour vs. colour) or points of view. Though the various language editions are held to global policies such as "neutral point of view," they diverge on some points of policy and practice, most notably on whether images that are not licensed freely may be used under a claim of fair use.

Wales has described Wikipedia as "an effort to create and distribute a free encyclopedia of the highest possible quality to every single person on the planet in their own language." Though each language edition functions more or less independently, some efforts are made to supervise them all. They are coordinated in part by Meta-Wiki, the Wikimedia Foundation's wiki devoted to maintaining all of its projects (Wikipedia and others). For instance, Meta-Wiki provides important statistics on all language editions of Wikipedia, and it maintains a list of articles every Wikipedia should have. The list concerns basic content by subject: biography, history, geography, society, culture, science, technology, and mathematics. As for the rest, it is not rare for articles strongly related to a particular language not to have counterparts in another edition. For example, articles about small towns in the United States might only be available in English, even when they meet notability criteria of other language Wikipedia projects.

Translated articles represent only a small portion of articles in most editions, in part because fully automated translation of articles is disallowed. Articles available in more than one language may offer " Interwiki links", which link to the counterpart articles in other editions.

History

Wikipedia began as a complementary project for Nupedia, a free online English-language encyclopedia project whose articles were written by experts and reviewed under a formal process. Nupedia was founded on March 9, 2000, under the ownership of Bomis, Inc, a web portal company. Its main figures were the Bomis CEO Wales and Larry Sanger, editor-in-chief for Nupedia and later Wikipedia. Nupedia was licensed initially under its own Nupedia Open Content License, switching to the GNU Free Documentation License before Wikipedia's founding at the urging of Richard Stallman. Sanger and Wales founded Wikipedia. While Wales is credited with defining the goal of making a publicly editable encyclopedia, Sanger is usually credited with the strategy of using a wiki to reach that goal. On January 10, 2001, Sanger proposed on the Nupedia mailing list to create a wiki as a "feeder" project for Nupedia. Wikipedia was formally launched on January 15, 2001, as a single English-language edition at www.wikipedia.com, and announced by Sanger on the Nupedia mailing list. Wikipedia's policy of "neutral point-of-view" was codified in its initial months, and was similar to Nupedia's earlier "nonbiased" policy. Otherwise, there were relatively few rules initially and Wikipedia operated independently of Nupedia.

Number of articles in the English Wikipedia (in blue)

Wikipedia gained early contributors from Nupedia, Slashdot postings, and web search engine indexing. On August 8, 2001, Wikipedia had over 8,000 articles. On September 25, 2001, Wikipedia had over 13,000 articles. And by the end of 2001 it had grown to approximately 20,000 articles and 18 language editions. By late 2002, it had reached 26 language editions, 46 by the end of 2003, and 161 by the final days of 2004. Nupedia and Wikipedia coexisted until the former's servers were taken down permanently in 2003, and its text was incorporated into Wikipedia. English Wikipedia passed the two million-article mark on September 9, 2007, making it the largest encyclopedia ever assembled, surpassing even the 1407 Yongle Encyclopedia, which had held the record for 600 years.

Citing fears of commercial advertising and lack of control in Wikipedia, users of the Spanish Wikipedia forked from Wikipedia to create the Enciclopedia Libre in February 2002. These moves encouraged Wales to announce that Wikipedia would not display advertisements, and to change Wikipedia's domain from wikipedia.com to wikipedia.org.

Growth of the number of articles in the English Wikipedia (in blue)

Though the English Wikipedia reached three million articles in August 2009, the growth of the edition, in terms of the numbers of articles and of contributors, appears to have peaked around early 2007. Around 1,800 articles were added daily to the encyclopedia in 2006; by 2013 that average was roughly 800. A team at the Palo Alto Research Centre attributed this slowing of growth to the project's increasing exclusivity and resistance to change. Others suggest that the growth is flattening naturally because articles that could be called ' low-hanging fruit' – topics that clearly merit an article – have already been created and built up extensively.

In November 2009, a researcher at the Rey Juan Carlos University in Madrid found that the English Wikipedia had lost 49,000 editors during the first three months of 2009; in comparison, the project lost only 4,900 editors during the same period in 2008. The Wall Street Journal cited the array of rules applied to editing and disputes related to such content among the reasons for this trend. Wales disputed these claims in 2009, denying the decline and questioning the methodology of the study. Two years later, Wales acknowledged the presence of a slight decline, noting a decrease from "a little more than 36,000 writers" in June 2010 to 35,800 in June 2011. Nevertheless, in the same interview, he claimed the number of editors was "stable and sustainable". In July 2012, the Atlantic reported that the number of administrators is also in decline.

In January 2007, Wikipedia entered for the first time the top-ten list of the most popular websites in the United States, according to comScore Networks Inc. With 42.9 million unique visitors, Wikipedia was ranked No. 9, surpassing the New York Times (#10) and Apple Inc. (#11). This marked a significant increase over January 2006, when the rank was No. 33, with Wikipedia receiving around 18.3 million unique visitors. As of December 2012, Wikipedia is the sixth-most-popular website worldwide according to Alexa Internet, receiving more than 2.7 billion U.S. pageviews every month, out of a global monthly total of over 12 billion pageviews.

On January 18, 2012, the English Wikipedia participated in a series of coordinated protests against two proposed laws in the United States Congress—the Stop Online Piracy Act (SOPA) and the PROTECT IP Act (PIPA)—by blacking out its pages for 24 hours. More than 162 million people viewed the blackout explanation page that temporarily replaced Wikipedia content.

Loveland and Reagle argue that, in process, Wikipedia follows a long tradition of historical encyclopedias that accumulated improvements piecemeal through " stigmergic accumulation".

Analysis of content

Although poorly written articles are flagged for improvement, critics note that the style and quality of individual articles may vary greatly. Others argue that inherent biases (willful or not) arise in the presentation of facts, especially controversial topics and public or historical figures. Although Wikipedia's stated mission is to provide information and not argue value judgements, articles often contain overly specialized, trivial, or objectionable material.

In 2006, the Wikipedia Watch criticism website listed dozens of examples of plagiarism by Wikipedia editors on the English version. Wales has said in this respect: "We need to deal with such activities with absolute harshness, no mercy, because this kind of plagiarism is 100% at odds with all of our core principles."

Accuracy of content

Articles for traditional encyclopedias such as Encyclopædia Britannica are carefully and deliberately written by experts, lending such encyclopedias a reputation for accuracy. Conversely, Wikipedia is often cited for factual inaccuracies and misrepresentations. However, a non-scientific report in the journal Nature in 2005 suggested that for some scientific articles Wikipedia came close to the level of accuracy of Encyclopædia Britannica and had a similar rate of "serious errors." These claims have been disputed by, among others, Encyclopædia Britannica. Although Nature gave a point by point rebuttal of Britannica's argument, the Nature report did agree that the structure of Wikipedia's articles was often poor.

As a consequence of the open structure, Wikipedia "makes no guarantee of validity" of its content, since no one is ultimately responsible for any claims appearing in it. Concerns have been raised regarding the lack of accountability that results from users' anonymity, the insertion of false information, vandalism, and similar problems.

Economist Tyler Cowen wrote: "If I had to guess whether Wikipedia or the median refereed journal article on economics was more likely to be true, after a not so long think I would opt for Wikipedia." He comments that some traditional sources of non-fiction suffer from systemic biases and novel results, in his opinion, are over-reported in journal articles and relevant information is omitted from news reports. However, he also cautions that errors are frequently found on Internet sites, and that academics and experts must be vigilant in correcting them.

Critics argue that Wikipedia's open nature and a lack of proper sources for most of the information makes it unreliable. Some commentators suggest that Wikipedia may be reliable, but that the reliability of any given article is not clear. Editors of traditional reference works such as the Encyclopædia Britannica have questioned the project's utility and status as an encyclopedia.

Wikipedia's open structure inherently makes it an easy target for Internet trolls, spamming, and those with an agenda to push. The addition of political spin to articles by organizations including members of the US House of Representatives and special interest groups has been noted, and organizations such as Microsoft have offered financial incentives to work on certain articles. For example, in August 2007, the website WikiScanner began to trace the sources of changes made to Wikipedia by anonymous editors without Wikipedia accounts. The program revealed that many such edits were made by corporations or government agencies changing the content of articles related to them, their personnel or their work. These issues have been parodied, notably by Stephen Colbert on The Colbert Report.

Quality of writing

Because contributors usually rewrite small portions of an entry rather than making full-length revisions, high- and low-quality content may be intermingled within an entry. Roy Rosenzweig, a history professor, stated that American National Biography Online outperformed Wikipedia in terms of its "clear and engaging prose", which, he said, was an important aspect of good historical writing. Contrasting Wikipedia's treatment of Abraham Lincoln to that of Civil War historian James McPherson in American National Biography Online, he said that both were essentially accurate and covered the major episodes in Lincoln's life, but praised "McPherson's richer contextualization... his artful use of quotations to capture Lincoln's voice ... and ... his ability to convey a profound message in a handful of words." By contrast, he gives an example of Wikipedia's prose that he finds "both verbose and dull". Rosenzweig also criticized the "waffling—encouraged by the npov policy—[which] means that it is hard to discern any overall interpretive stance in Wikipedia history." By example, he quoted the conclusion of Wikipedia's article on William Clarke Quantrill. While generally praising the article, he pointed out its "waffling" conclusion: "Some historians...remember him as an opportunistic, bloodthirsty outlaw, while others continue to view him as a daring soldier and local folk hero."

Other critics have made similar charges that, even if Wikipedia articles are factually accurate, they are often written in a poor, almost unreadable style. Frequent Wikipedia critic Andrew Orlowski commented: "Even when a Wikipedia entry is 100 per cent factually correct, and those facts have been carefully chosen, it all too often reads as if it has been translated from one language to another then into to a third, passing an illiterate translator at each stage." A study of cancer articles by Yaacov Lawrence of the Kimmel Cancer Centre at Thomas Jefferson University found that the entries were mostly accurate, but they were written at college reading level, as opposed to the ninth grade level seen in the Physician Data Query. He said that "Wikipedia's lack of readability may reflect its varied origins and haphazard editing." The Economist argued that better-written articles tend to be more reliable: "inelegant or ranting prose usually reflects muddled thoughts and incomplete information."

Coverage of topics and systemic bias

Wikipedia seeks to create a summary of all human knowledge in the form of an online encyclopedia, with each topic of knowledge covered encyclopedically in one article. Since it has terabytes of disk space, it can have far more topics than can be covered by any conventional printed encyclopedia. It also contains materials that some people may find objectionable, offensive, or pornographic (cf below). It was made clear that this policy is not up for debate, and the policy has sometimes proved controversial. For instance, in 2008, Wikipedia rejected an online petition against the inclusion of Muhammad's depictions in its English edition, citing this policy. The presence of politically, religiously, and pornographically sensitive materials in Wikipedia has led to the censorship of Wikipedia by national authorities in China, Pakistan and the United Kingdom, among other countries. In addition, Larry Sanger, co-founder of Wikipedia, has criticized Wikipedia not for the pornographic content, but for the fact that the content is accessible to children, and contains extreme and detailed photographs and films.

A 2008 study conducted by researchers at Carnegie Mellon University and Palo Alto Research Centre gave a distribution of topics as well as growth (from July 2006 to January 2008) in each field:

Pie chart of Wikipedia content by subject as of January 2008

Culture and the arts: 30% (210%)

Biographies and persons: 15% (97%)

Geography and places: 14% (52%)

Society and social sciences: 12% (83%)

History and events: 11% (143%)

Natural and physical sciences: 9% (213%)

Technology and the applied sciences: 4% (−6%)

Religions and belief systems: 2% (38%)

Health: 2% (42%)

Mathematics and logic: 1% (146%)

Thought and philosophy: 1% (160%)

These numbers refer only to the quantity of articles: it is possible for one topic to contain a large number of short articles and another to contain a small number of large ones. Through its "Wikipedia Loves Libraries" program, Wikipedia has partnered with major public libraries such as the New York Public Library for the Performing Arts to expand its coverage of underrepresented subjects and articles.

Furthermore, the exact coverage of Wikipedia is under constant review by the editors, and disagreements are not uncommon (see also deletionism and inclusionism).

As of September 2009, Wikipedia articles cover about half a million places on Earth. However, research conducted by the Oxford Internet Institute has shown that the geographic distribution of articles is highly uneven. Most articles are written about North America, Europe, and East Asia, with very little coverage of large parts of the developing world, including most of Africa.

When multiple editors contribute to one topic or set of topics, there may arise a systemic bias, such as non-opposite definitions for apparent antonyms. In 2011 Wales noted that the unevenness of coverage is a reflection of the demography of the editors, which predominantly consists of young males with high education levels in the developed world (cf. above) Systemic bias on Wikipedia may follow that of culture generally, for example favouring certain ethnicities or majority religions. It may more specifically follow the biases of Internet culture, inclining to being young, male, English speaking, educated, technologically aware, and wealthy enough to spare time for editing. Biases of its own may include over-emphasis on topics such as pop culture, technology, and current events.

A "selection bias" may arise when more words per article are devoted to one public figure than a rival public figure. Editors may dispute suspected biases and discuss controversial articles, sometimes at great length. Wales has noted the dangers of bias on controversial political topics or polarizing public figures.

Citing Wikipedia

Most university lecturers discourage students from citing any encyclopedia in academic work, preferring primary sources; some specifically prohibit Wikipedia citations. Wales stresses that encyclopedias of any type are not usually appropriate to use as citeable sources, and should not be relied upon as authoritative. Wales once said he receives about ten e-mails weekly from students saying they got failing grades on papers because they cited Wikipedia; he told the students they got what they deserved. "For God's sake, you're in college; don't cite the encyclopedia", he said.

In February 2007 an article in The Harvard Crimson newspaper reported that a few of the professors at Harvard University include Wikipedia in their syllabi, but that there is a split in their perception of using Wikipedia. In June 2007 former president of the American Library Association Michael Gorman condemned Wikipedia, along with Google, stating that academics who endorse the use of Wikipedia are "the intellectual equivalent of a dietitian who recommends a steady diet of Big Macs with everything." He also said that "a generation of intellectual sluggards incapable of moving beyond the Internet" was being produced at universities. He complains that the web-based sources are discouraging students from learning from the more rare texts which are found only on paper or subscription-only web sites. In the same article Jenny Fry (a research fellow at the Oxford Internet Institute) commented on academics who cite Wikipedia, saying that: "You cannot say children are intellectually lazy because they are using the Internet when academics are using search engines in their research. The difference is that they have more experience of being critical about what is retrieved and whether it is authoritative. Children need to be told how to use the Internet in a critical and appropriate way."

A Harvard Law textbook, Legal Research in a Nutshell (2011), cites Wikipedia as a "general source" that "can be a real boon" in "coming up to speed in the law governing a situation" and, "while not authoritative, can provide basic facts as well as leads to more in-depth resources."

Operation

Software and hardware

The operation of Wikipedia depends on MediaWiki, a custom-made, free and open source wiki software platform written in PHP and built upon the MySQL database system. The software incorporates programming features such as a macro language, variables, a transclusion system for templates, and URL redirection. MediaWiki is licensed under the GNU General Public License and it is used by all Wikimedia projects, as well as many other wiki projects. Originally, Wikipedia ran on UseModWiki written in Perl by Clifford Adams (Phase I), which initially required CamelCase for article hyperlinks; the present double bracket style was incorporated later. Starting in January 2002 (Phase II), Wikipedia began running on a PHP wiki engine with a MySQL database; this software was custom-made for Wikipedia by Magnus Manske. The Phase II software was repeatedly modified to accommodate the exponentially increasing demand. In July 2002 (Phase III), Wikipedia shifted to the third-generation software, MediaWiki, originally written by Lee Daniel Crocker. Several MediaWiki extensions are installed to extend the functionality of the MediaWiki software. In April 2005 a Lucene extension was added to MediaWiki's built-in search and Wikipedia switched from MySQL to Lucene for searching. The site currently uses Lucene Search 2.1, which is written in Java and based on Lucene library 2.3.

Overview of system architecture, December 2010. See server layout diagrams on Meta-Wiki.

Wikipedia receives between 25,000 and 60,000 page requests per second, depending on time of day. Page requests are first passed to a front-end layer of Squid caching servers. Further statistics are available based on a publicly available 3-months Wikipedia access trace. Requests that cannot be served from the Squid cache are sent to load-balancing servers running the Linux Virtual Server software, which in turn pass the request to one of the Apache web servers for page rendering from the database. The web servers deliver pages as requested, performing page rendering for all the language editions of Wikipedia. To increase speed further, rendered pages are cached in a distributed memory cache until invalidated, allowing page rendering to be skipped entirely for most common page accesses.

Wikipedia employed a single server until 2004, when the server setup was expanded into a distributed multitier architecture. In January 2005, the project ran on 39 dedicated servers in Florida. This configuration included a single master database server running MySQL, multiple slave database servers, 21 web servers running the Apache HTTP Server, and seven Squid cache servers. Wikipedia currently runs on dedicated clusters of Linux servers (mainly Ubuntu), with a few OpenSolaris machines for ZFS. As of December 2009, there were 300 in Florida and 44 in Amsterdam.

Access to content

Content licensing

When the project was started in 2001, all text in Wikipedia was covered by GNU Free Documentation License (GFDL), a copyleft license permitting the redistribution, creation of derivative works, and commercial use of content while authors retain copyright of their work. GFDL was created for software manuals that come with free software programs that are licensed under GPL. This made it a poor choice for a general reference work; for example, the GFDL requires the reprints of materials from Wikipedia to come with a full copy of the GFDL license text. In December 2002, the Creative Commons license was released: it was specifically designed for creative works in general, not just for software manuals. The license gained popularity among bloggers and others distributing creative works on the Web. The Wikipedia project sought the switch to the Creative Commons. Because the two licenses, GFDL and Creative Commons, were incompatible, in November 2008, following the request of the project, the Free Software Foundation (FSF) released a new version of GFDL designed specifically to allow Wikipedia to relicense its content to CC BY-SA by August 1, 2009. (A new version of GFDL automatically covers Wikipedia contents.) In April 2009, Wikipedia and its sister projects held a community-wide referendum which decided the switch in June 2009.

The handling of media files (e.g., image files) varies across language editions. Some language editions, such as the English Wikipedia, include non-free image files under fair use doctrine, while the others have opted not to, in part due to the lack of fair use doctrines in their home countries (e.g., in Japanese copyright law). Media files covered by free content licenses (e.g., Creative Commons' CC BY-SA) are shared across language editions via Wikimedia Commons repository, a project operated by the Wikimedia Foundation. Wikipedia's accommodation of varying international copyright laws regarding images has led some to observe that its photographic coverage of topics lags behind the quality of the encyclopedic text.

The Wikimedia Foundation is not a licensor of content, but merely a hosting service for the contributors (and licensors) of the Wikipedia. This position has been successfully defended in court.

Methods of access

Because Wikipedia content is distributed under an open license, anyone can reuse or re-distribute it at no charge. The content of Wikipedia has been published in many forms, both online and offline, outside of the Wikipedia website.

Web sites – Thousands of " mirror sites" exist that republish content from Wikipedia: two prominent ones, that also include content from other reference sources, are Reference.com and Answers.com. Another example is Wapedia, which began to display Wikipedia content in a mobile-device-friendly format before Wikipedia itself did.

Search engines – Some web search engines make special use of Wikipedia content when displaying search results: examples include Bing (via technology gained from Powerset) and Duck Duck Go.

Compact Discs, DVDs – Collections of Wikipedia articles have been published on optical discs. An English version, 2006 Wikipedia CD Selection, contained about 2,000 articles. The Polish-language version contains nearly 240,000 articles. There are German and Spanish-language versions as well. Also, "Wikipedia for Schools", the Wikipedia series of CDs/DVDs produced by Wikipedians and SOS Children, is a free, hand-checked, non-commercial selection from Wikipedia targeted around the UK National Curriculum and intended to be useful for much of the English-speaking world. The project is available online; an equivalent print encyclopedia would require roughly 20 volumes.

Books – There are efforts to put a select subset of Wikipedia's articles into printed book form. Since 2009, tens of thousands of print on demand books which reproduced English, German, Russian and French Wikipedia articles have been produced by the American company Books LLC and by three Mauritian subsidiaries of the German publisher VDM.

Semantic Web – The website DBpedia, begun in 2007, is a project that extracts data from the infoboxes and category declarations of the English-language Wikipedia and makes it available in a queriable semantic format, RDF. The possibility has also been raised to have Wikipedia export its data directly in a semantic format, possibly by using the Semantic MediaWiki extension. Such an export of data could also help Wikipedia reuse its own data, both between articles on the same language Wikipedia and between different language Wikipedias.

Obtaining the full contents of Wikipedia for reuse presents challenges, since direct cloning via a web crawler is discouraged. Wikipedia publishes " dumps" of its contents, but these are text-only; as of 2007 there is no dump available of Wikipedia's images.

Several languages of Wikipedia also maintain a reference desk, where volunteers answer questions from the general public. According to a study by Pnina Shachaf in the Journal of Documentation, the quality of the Wikipedia reference desk is comparable to a standard library reference desk, with an accuracy of 55%.

Mobile access

Wikipedia's original medium was for users to read and edit content using any standard web browser through a fixed internet connection. In addition, Wikipedia content is now accessible through the mobile web.

Access to Wikipedia from mobile phones was possible as early as 2004, through the Wireless Application Protocol (WAP), via the Wapedia service. In June 2007 Wikipedia launched en.mobile.wikipedia.org, an official website for wireless devices. In 2009 a newer mobile service was officially released, located at en.m.wikipedia.org, which caters to more advanced mobile devices such as the iPhone, Android-based devices or WebOS-based devices. Several other methods of mobile access to Wikipedia have emerged. Many devices and applications optimise or enhance the display of Wikipedia content for mobile devices, while some also incorporate additional features such as use of Wikipedia metadata (See Wikipedia:Metadata), such as geoinformation.

Wikipedia Zero is an initiative of the Wikimedia Foundation to expand the reach of the encyclopedia to the developing countries.

Impact

Impact on publishing

Some observers have stated that Wikipedia represents an economic threat to publishers of traditional encyclopedias, who may be unable to compete with a product that is essentially free. Nicholas Carr wrote a 2005 essay, "The amorality of Web 2.0", that criticized websites with user-generated content, like Wikipedia, for possibly leading to professional (and, in his view, superior) content producers going out of business, because "free trumps quality all the time." Carr wrote, "Implicit in the ecstatic visions of Web 2.0 is the hegemony of the amateur. I for one can't imagine anything more frightening." Others dispute the notion that Wikipedia, or similar efforts, will entirely displace traditional publications. For instance, Chris Anderson, the editor-in-chief of Wired Magazine, wrote in Nature that the " wisdom of crowds" approach of Wikipedia will not displace top scientific journals, with their rigorous peer review process.

Cultural significance

Graph showing the number of days between every 10,000,000th edit.

In addition to logistic growth in the number of its articles, Wikipedia has steadily gained status as a general reference website since its inception in 2001. According to Alexa and comScore, Wikipedia is among the ten most visited websites worldwide. The growth of Wikipedia has been fueled by its dominant position in Google search results; about 50% of search engine traffic to Wikipedia comes from Google, a good portion of which is related to academic research. The number of readers of Wikipedia worldwide reached 365 million at the end of 2009. The Pew Internet and American Life project found that one third of US Internet users consulted Wikipedia. In October 2006, the site was estimated to have a hypothetical market value of $580 million if it ran advertisements.

Wikipedia's content has also been used in academic studies, books, conferences, and court cases. The Parliament of Canada's website refers to Wikipedia's article on same-sex marriage in the "related links" section of its "further reading" list for the Civil Marriage Act. The encyclopedia's assertions are increasingly used as a source by organizations such as the U.S. Federal Courts and the World Intellectual Property Organization – though mainly for supporting information rather than information decisive to a case. Content appearing on Wikipedia has also been cited as a source and referenced in some U.S. intelligence agency reports. In December 2008, the scientific journal RNA Biology launched a new section for descriptions of families of RNA molecules and requires authors who contribute to the section to also submit a draft article on the RNA family for publication in Wikipedia.

Wikipedia has also been used as a source in journalism, often without attribution, and several reporters have been dismissed for plagiarizing from Wikipedia. In July 2007 Wikipedia was the focus of a 30-minute documentary on BBC Radio 4 which argued that, with increased usage and awareness, the number of references to Wikipedia in popular culture is such that the term is one of a select band of 21st-century nouns that are so familiar (Google, Facebook, YouTube) that they no longer need explanation and are on a par with such 20th-century terms as Hoovering or Coca-Cola.

On September 28, 2007, Italian politician Franco Grillini raised a parliamentary question with the Minister of Cultural Resources and Activities about the necessity of freedom of panorama. He said that the lack of such freedom forced Wikipedia, "the seventh most consulted website" to forbid all images of modern Italian buildings and art, and claimed this was hugely damaging to tourist revenues.

On September 16, 2007, The Washington Post reported that Wikipedia had become a focal point in the 2008 U.S. election campaign, saying, "Type a candidate's name into Google, and among the first results is a Wikipedia page, making those entries arguably as important as any ad in defining a candidate. Already, the presidential entries are being edited, dissected and debated countless times each day." An October 2007 Reuters article, titled "Wikipedia page the latest status symbol," reported the recent phenomenon of how having a Wikipedia article vindicates one's notability.

Active participation also has an impact. Law students have been assigned to write Wikipedia articles as an exercise in clear and succinct writing for an uninitiated audience.

Awards

Wikipedia won two major awards in May 2004. The first was a Golden Nica for Digital Communities of the annual Prix Ars Electronica contest; this came with a €10,000 (£6,588; $12,700) grant and an invitation to present at the PAE Cyberarts Festival in Austria later that year. The second was a Judges' Webby Award for the "community" category. Wikipedia was also nominated for a "Best Practices" Webby. On January 26, 2007, Wikipedia was also awarded the fourth highest brand ranking by the readers of brandchannel.com, receiving 15% of the votes in answer to the question "Which brand had the most impact on our lives in 2006?"

In September 2008, Wikipedia received Quadriga A Mission of Enlightenment award of Werkstatt Deutschland along with Boris Tadić, Eckart Höfling, and Peter Gabriel. The award was presented to Wales by David Weinberger.

Satire

Many parody Wikipedia's openness and susceptibility to inserted inaccuracies, with characters vandalizing or modifying the online encyclopedia project's articles.

Comedian Stephen Colbert has parodied or referenced Wikipedia on numerous episodes of his show The Colbert Report and coined the related term wikiality, meaning "together we can create a reality that we all agree on—the reality we just agreed on". Another example can be found in a front-page article in The Onion in July 2006, with the title "Wikipedia Celebrates 750 Years of American Independence". " My Number One Doctor", a 2007 episode of the TV show Scrubs, played on the perception that Wikipedia is an unreliable reference tool with a scene in which Dr. Perry Cox reacts to a patient who says that a Wikipedia article indicates that the raw food diet reverses the effects of bone cancer by retorting that the same editor who wrote that article also wrote the Battlestar Galactica episode guide. In 2008, the comedic website CollegeHumor produced a video sketch named "Professor Wikipedia", in which the fictitious Professor Wikipedia instructs a class with a medley of unverifiable and occasionally absurd statements.

The Dilbert comic strip from May 8, 2009, concludes with Topper suggesting that the others check Wikipedia in a few minutes (after he's had a chance to edit it in order to back up a preposterous claim regarding a gallstone).

In July 2009, BBC Radio 4 broadcast a comedy series called Bigipedia, which was set on a website which was a parody of Wikipedia. Some of the sketches were directly inspired by Wikipedia and its articles.

In 2010, comedian Daniel Tosh encouraged viewers of his show, Tosh.0, to visit the show's Wikipedia article and edit it at will. On a later episode, he commented on the edits to the article, most of them offensive, which had been made by the audience and had prompted the article to be locked from editing.

Scientific use

In computational linguistics, information retrieval and natural language processing, Wikipedia has seen widespread use as a corpus for linguistic research. In particular, it commonly serves as a target knowledge base for the entity linking problem, which is then called "wikification", and to the related problem of word sense disambiguation. Methods similar to wikification can in turn be used to find "missing" links in Wikipedia.

Related projects

A number of interactive multimedia encyclopedias incorporating entries written by the public existed long before Wikipedia was founded. The first of these was the 1986 BBC Domesday Project, which included text (entered on BBC Micro computers) and photographs from over 1 million contributors in the UK, and covered the geography, art, and culture of the UK. This was the first interactive multimedia encyclopedia (and was also the first major multimedia document connected through internal links), with the majority of articles being accessible through an interactive map of the UK. The user interface and part of the content of the Domesday Project were emulated on a website until 2008. One of the most successful early online encyclopedias incorporating entries by the public was h2g2, which was created by Douglas Adams. The h2g2 encyclopedia is relatively light-hearted, focusing on articles which are both witty and informative. Everything2 was created in 1998. All of these projects had similarities with Wikipedia, but were not wikis and neither gave full editorial privileges to public users.

GNE, an encyclopedia which was not a wiki, also created in January 2001, co-existed with Nupedia and Wikipedia early in its history; however, it has been retired.

Other websites centered on collaborative knowledge base development have drawn inspiration from Wikipedia. Some, such as Susning.nu, Enciclopedia Libre, Hudong, and Baidu Baike likewise employ no formal review process, although some like Conservapedia are not as open. Others use more traditional peer review, such as Encyclopedia of Life and the online wiki encyclopedias Scholarpedia and Citizendium. The latter was started by Sanger in an attempt to create a reliable alternative to Wikipedia. Scholarpedia also focuses on ensuring high quality.